Known in the art are numerous methods for processing of phosphorus slime. Mostly used now are methods contemplating combustion of slimes at the temperature of 1,000.degree. C. Used for combustion are slimes with a content of phosphorus of at least 50% by weight. Slimes containing 15 to 50% by weight of phosphorus are processed by distillation. Distilling-off of phosphorus is effected by means of superheated steam at a temperature within the range of from 160.degree. to 175.degree. C. under a pressure of from 6 to 8 atm. Known methods for processing of "thin" phosphorus-containing slimes by distillation, filtration, centrifugation or briquetting feature low efficiency, necessitate high expenses for their commercial implementation and cannot provide for utilization of all the products involved in the processing.
Known in the art are also methods for breaking slimes by means of inorganic salts and acids. Thus, U.S. Pat. No. 3,515,515 teaches breaking of slime at a temperature of from 40.degree. to 70.degree. C. by means of water-soluble compounds of hexavalent chromium, i.e. chromates and bichromates of metals, and sulphuric acid. The method contemplates the use of a solution of chromates with a concentration of from 0.1 to 10.0% by weight as calculated per chromic acid. Sulphuric acid is added to chromic acid at the ratio of 1:1.
Another U.S. Pat. No. 3,442,621 teaches processing of slime with chromic acid in a concentration of from 0.1 to 10.0% by weight of water in the slime and with hydrochloric acid or sulphuric acid in a concentration of from 1 to 30% by weight of water in the slime.
Upon the action of reagents, the protective film stabilizing the slime particles is oxidized and the slime structure is broken.
As a result, pure yellow phosphorus is obtained along with a small amount of phosphoric acid and a solid residue. The resulting pure phosphorus is collected and combusted by a conventional method to give phosphoric acid.
These prior art methods, however, have the following disadvantages: formation of substantial amounts of liquid wastes containing a suspension of solid particles, weak phosphoric and sulphuric acids, chromium salts or chromic acid; pollution of the environment with the accumulated liquid wastes; high cost of chromium compounds employed in the process and irrevocable losses thereof.
German Democratic Republic Pat. No. 54677 of Mar. 20, 1967 teaches the treatment of a phosphorus slime with an alkali. In doing so, about 30% of phosphorus contained in the slime is converted to a poisonous gas phosphine, while the remaining part of phosphorus remains in the form of a black, strongly contaminated phosphite solution (Na.sub.2 NPO.sub.3). This prior art method has a disadvantage residing in the formation of large amounts of phosphine which should be further entrapped, as well as the formation of solid and liquid wastes polluting the environment. While effective methods exist for processing of "thick" slimes, there are still no such methods for processing of "thin" slimes.
Known in the art are numerous methods for processing the off-gases resulting from the manufacture of phosphorus by way of trapping phosphine therefrom by using various absorption solutions. These absorption solutions contain CuCl, FeCl.sub.2, HCl, HgCl.sub.2 +HCl, H.sub.2 SO.sub.4 +Na.sub.2 Cr.sub.2 O.sub.7, H.sub.2 SO.sub.4 +(NH.sub.4).sub.2 SO.sub.4, NaClO.sub.2 +Cl.sub.2, NaClO.sub.2 +bleaching powder; HNO.sub.3 ;HNO.sub.3 +AgNO.sub.3 ; AsCl.sub.3, FeCl.sub.3, KMnO.sub.4 and the like.
U.S. Pat. No. 2,673,885 teaches a method for purification of the gases in a counter-current scrubber, which comprises washing of the gases with chlorinated water containing 0.3 to 1 g/l of chlorine.
Among the above-mentioned absorption solutions such solutions as CuCl, FeCl.sub.2, HCl, HNO.sub.3, FeCl.sub.3 have a small absorption capacity with respect to phosphine. Solutions containing HgCl.sub.2 +HCl, AsCl.sub.3 or NaCl0.sub.2 +bleaching powder are poisonous or evolve a poisonous gas, i.e. chlorine. The solution containing HNO.sub.3 +AgNO.sub.3, though quite efficient, is rather expensive.
The products obtained with the use of said solutions do not find any use, they are discarded as wastes and pollute the environment.
Despite a great number of patents and other publications in the art there are no cheap, effecive methods for processing or "thin" slimes and off-gases resulting from the manufacture of phosphorus which would make full utilization of all the products of such processing. Also, there are no cheap methods for utilization of Cottrell dust or phosphorite fines. For this reason, at the present time processing of "thin" slimes, entrapping of phosphine and phosphorus particles from off-gases, a more rational utilization of Cottrell dust and phosphorite fines constitute an urgent but still unsolved problem.